1. Field of the Invention
This invention relates to an image forming apparatus, such as an electrophotographic printer, for forming an image on an image bearing member and, more particularly, to an image forming apparatus having a disordering and charging device for disordering a developing agent remaining on the image bearing member and for uniformly charging the image bearing member.
2. Description of Related Information
Generally, in conventional image forming apparatus, a surface of an image bearing member, such as a photosensitive drum, is charged by a main charger. The entire surface of the drum is charged by the main charger. Then, a latent image is formed on the image bearing member. A developing device then develops the latent image using a developing agent (toner) to make the latent image visible. Subsequently, the developed image is transferred onto a medium such as a paper sheet by a transferring device. Most of the toner of the developed image on the image bearing member is transferred onto the paper sheet by the transferring device during the image transfer process. However, some portion of the toner of the developed image remains on the image bearing member after the transfer of the developed image to the paper sheet by the transferring device. Thus, the residual toner particles on the image bearing member are typically removed from the image bearing member by a cleaning device.
Recently, in the art of image forming apparatus development there has been recognized a need to reduce the size of the apparatus into a more compact housing. For example, to this end, U.S. Pat. No. 4,769,676 discloses an image forming apparatus having a device which simultaneously performs the developing process and the cleaning process. The image forming cycle of the apparatus is performed within one rotation of its image bearing member. Thus, use of this developing and cleaning device has reduced the size of the image forming apparatus since an image bearing member can be used that has a reduced diameter. The disclosed device, which serves as both a developing device and a cleaning device, does not require, for example, as much of the circumference of the drum which forms the image bearing member.
Further, this image forming apparatus includes a disordering device positioned before a main charger. This disordering device disorders the residual toner image remaining on the image bearing member after the transfer of the developed image to a medium and before the next image forming operation. The disordering device includes a conductive member (a conductive roller or a conductive brush) which is in sliding contact with the image bearing member. The conductive member has applied to it a bias voltage. Therefore, by sliding contact between the conductive member and the image bearing member, the residual toner is temporarily attracted to the conductive member and is then deposited over other parts of the surface of the image bearing member. Thereby, the residual toner is disordered. Any residual toner image is made non-patterned and loses its original appearance.
Moreover, furthering an objective of the present invention to reduce the size of image forming apparatus into a more compact housing, there are related applications of the same inventor (U.S. applications Ser. No. 531,245 filed May 31, 1990 and Ser. No. 694,761 filed in May 2, 1991). These disclose a disordering and charging device which performs both the functions of charging and disordering in a single conductive member. Thus, in this disordering and charging device, comprising a single conductive member, the need for a separate main charger as shown in U.S. Pat. No. 4,769,676 is eliminated.
However, in the disordering and charging device according to these disclosures, since both the function of charging and disordering is performed by the single conductive member, it is very difficult to sufficiently disorder the residual toner image and to uniformly charge the surface of the image bearing member. Thus, a residual toner image can still remain in the next image forming process. Consequently, the next image forming cycle may be carried out so that the new image to be transferred is superimposed on the residual toner image remaining on the image bearing member. Furthermore, the surface of the image bearing member may not be uniformly charged. Consequently, the new resulting image formed in the next image forming process is deteriorated. For example, it may be streaked from the non-uniform charging.